Elimination of electric-pop noise in MR/GMR device

ABSTRACT

The invention relates to a magnetoresistive device comprising: a bottom shield; a top shield; an AMR/GMR device; a first insulating gap layer between said bottom shield and said AMR/GMR; a second insulating gap layer between said AMR/GMR and said top shield; and conductive layer contacting electrically both said AMR/GMR device to said bottom shield. Furthermore, similar active devices free of electric-pop noise also be disclosed.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention generally relates to an active devicecapable of converting an electrical signal into a voltage, morespecifically, to a soft-adjacent magnetic transverse bias layer(hereinafter referred to as SAL) biased magnetic recording head withinsulator spacer.

[0003] 2. Description of the Related Art

[0004] As is well known in the field, the insulating spacer in ananisotropic magneto-resistive/a giant magneto-resistive device(hereinafter referred to as AMR/GMR) used for magnetic recording isbecoming thinner and thinner in order to increase a linear recordingdensity. Inevitably, we are facing electric-pop noise resulting from thethinner spacer. For high manufacturing yield and reliability of electricand magnetic performance, such electric-pop noise must be eliminated.

[0005] U.S. Pat. No. 3,864,751 entitled “Induced Bias Magneto-resistiveRead Transducer” issued to Beaulier and Napela, on Feb. 4, 1975 proposedthat a SAL is isolated from a magneto-resistive device (referred to asMR hereinafter). The patent did not reveal any methods how to make it.Another key point is that the MR and SAL are electrically isolated. Inthe prior art described by Beaulieu et al., electric-pop noise ispresent if a thinner insulating spacer (<150 Å), such as Al₂O₃, is used.Otherwise, the devices would need a thicker SAL to bias the MR if athicker insulator spacer (2-400 Å) were used. There are two problemsassociated with the latter case. Firstly, the SAL can not be easilysaturated by a current in the MR and an antiferromagnetic pinning layermust be used to pin the SAL so that the SAL magnetization isperpendicular to the current direction. In this case, the device processbecomes very complicated and it also renders designs less extendible toa narrower shield to shield spacing for higher density recording.

[0006] The SAL has a function as a shunt bias layer in SAL biased AMRdevices. When the MR and SAL are spaced by electric conductingmaterials, such as Ta, the SAL and MR devices have the same electrictrack width. These configurations have been disclosed in U.S. Pat. No.4,663,685 issued in 1987, to C. Tsang, U.S. Pat. No. 4,639,806 issued in1987 to T. Kira, T. Miyagachi, and U.S. Pat. No. 5,108,037 issued to M.Yoshikawa, M. T. Krounbi, O. Voegeli and P. Wang.

SUMMARY OF THE INVENTION

[0007] Accordingly, one objective of this invention is to provide an AMRdesign with a thin insulating spacer free of electric-pop noise.

[0008] Another objective is to provide a SAL biased AMR product using aninsulated spacer.

[0009] A further objective of this invention is to provide an electricactive device free of electric-pop noise over an insulating spacer onthe top of an electric conductor.

[0010] Still another objective of this invention is to provide a designto eliminate electric-pop noise between an AMR/GMR active device andshields.

[0011] In accordance with one aspect of the present invention, amagnetoresistive device comprising:

[0012] a magnetoresistive layer;

[0013] a soft-adjacent magnetic transverse bias layer (SAL);

[0014] an insulating layer arranged between said magnetoresistive layerand said magnetic transverse bias layer;

[0015] a conductive layer contacting electrically both saidmagnetoresistive layer and said magnetic bias layer at at least one endregion of said SAL element.

[0016] In accordance with another aspect of the present invention, amagnetoresistive device comprising:

[0017] a first shield;

[0018] a second shield;

[0019] an AMR/GMR device;

[0020] a first insulating gap layer between said AMR/GMR and one of saidshields;

[0021] a second insulating gap layer between said AMR/GMR and another ofsaid two shields;

[0022] a conductive layer contacting electrically said AMR/GMR device toeither one of said shields.

[0023] In accordance with a further aspect of the present invention, ahard disk driver is provided with the magnetoresistive device.

[0024] Compared to the prior art by Tsang, Kire et al and Kroumbi et al,this invention provides an AMR sensor with much improved signal. Thesignal improvement can be as much as 90% provided that the same MR/SALdevice and operating current are used for the device.

[0025] Other objects, features and advantages of the present inventionwill become readily apparent from the following description taken inconjunction with the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

[0026] The accompanying drawings, which are incorporated in andconstitute a part of the specification, illustrate presently preferredembodiments of the invention, and together with the general descriptiongiven above and the detailed description of the preferred embodimentsgiven below, serve to explain the principles of the invention.

[0027]FIG. 1a is a diagram of a preferred embodiment of the invention,

[0028]FIG. 1b is a cross-section view taken along line AA indicated inFIG. 1a,

[0029]FIG. 2 is a diagram of an alternative embodiment of the invention,

[0030]FIG. 3 shows electric-pop test results before and after MR and SALare connected by microfabrication,

[0031]FIG. 4 shows an extension to prevent a MR/GMR device fromelectric-pop noise due to discharge between the MR/GMR device andshields.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0032] Embodiments according to the present invention will be describedin the following.

[0033]FIG. 1a is a diagram of a first preferred embodiment of theinvention. As shown in this figure, MR layer 10 and SAL 30 are separatedby a thin insulated spacer layer 20, and are electrically connected atthe ends of the MR element. An active region 10 of the MR device couldbe either a NiFe film or a composite layer, such as TaN/NiFe/TaN. NiFe,thickness ranges from 50 to 400 Å. Side regions 12 and 14 of the MRelement make electric contact with longitudinal bias layer and leadlayer 40 and 42. End regions 16 and 18 of the MR element are connectedto the end regions 32, 34 of SAL by leads. The length of MR element andSAL ranges from 2 to 20 μm. Insulating spacing layer 20 is made ofinsulating materials, such as Al₂O₃, AlON and SiO₂, and the typicalthickness of insulating spacing layer 20 varies from 50 to 200 Å.Soft-adjacent layer (SAL) 30 can be made of NiFe, NiFeCr, NiFeRh. Themoment ratio of SAL 30 to MR layer 10 ranges from 0.6 to 1.0.

[0034] In FIG. 1a, longitudinal bias layer 40 can be made ofanti-ferromagnetic materials, such as NiMn, FeMn, PtPdMn, IrMn and PtMn.Lead layer 42 can be made of Ta, W or Ta/Au/Ta. Longitudinal bias layer40 and lead layer 42 electrically contact with MR element 10 throughside regions 12 and 14, respectively. Therefore, the electric trackwidth of the MR element is defined by active region 10 as longitudinalbias layer 40 and lead layer 42 have much higher electric conductivitythan the MR layer.

[0035] On the other hand, longitudinal bias layer 40 and lead layer 42electrically contact with SAL layer 30 through side surfaces 32 and 34,respectively. Therefore, the electric track width of the SAL element isentire element width.

[0036] Now refer to FIG. 1b that shows cross-section view taken alongline AA indicated in FIG. 1a. Function of insulator films 50 is toprevent electric connection from MR 10 to SAL 30. Numeral 60 designatesan air-bearing surface (ABS).

[0037] In the following drawings, similar parts to those in FIG. 1 aredesignated by the same numerals as those used in FIG. 1. FIG. 2 shows analternative embodiment of the present invention. MR layer 10 and SAL 30are separated by a thin insulating spacer layer 30. MR layer 10 and SAL30 are electrically connected at only one end region of the MR element.In this embodiment, no electric current passes through the SAL element.However, the whole SAL element is in an equal electric potential to thatof one side of the MR element. One side region of the longitudinal biaslayer and the leader layer does not electrically contact with acorresponding SAL end region. Insulator films 52 are electricallyconnected between MR layer 10 and SAL 30 at one end of the trilayerelement device.

[0038]FIG. 3 shows test results of the electric-pop noise before andafter connection of MR layer 10 and SAL 30 under test conditions:trigger level=75 μV, threshold level=(Noise amplitude of Is=5 mA)+60 μV,and read current=12 mA.

[0039]FIGS. 3a and 3 b show electric-pop noise spectra of the devicebefore edge shorting of the MR and SAL element, and FIGS. 3c and 3 dshow the same of the device after edge shorting of the MR and SALelement.

[0040]FIG. 4 shows an extension to prevent a MR/GMR device fromelectric-pop noise due to discharge between the MR/GMR device andshields.

[0041]FIG. 4a is a diagram of a MR/GMR device that is electricallysorted to a bottom shield to prevent electric-pop noise due to staticdischarge between the MR/GMR device and a bottom shield.

[0042]FIG. 4b is a diagram of a MR/GMR device that is electricallysorted to a top shield to prevent electric-pop noise due to staticdischarge between the MR/GMR device and a top shield.

[0043] In FIGS. 4a and 4 b, reference numeral 60 designates an AMR or aGMR active device, the GMR device including a spin-valve, GMRmultilayer, and spin-dependent tunneling device, and numerals 62 and 64designate a longitudinal bias layer and a lead layer, respectively.Electric contact 66 is provided between one side of lead layer 64 and oflongitudinal bias layer 62 and the bottom shield 70. Bottom and topshields 70 and 80 are made of soft magnetic materials, such as NiFe.Gaps 72 and 74 are filled with electrically insulating materials, suchas Al₂O₃, AlNO, AlN, and vary from 250 to 2000 Å in thickness. Electriccontact 68 is provided between one side of lead layer 64 and oflongitudinal bias layer and top shield 80.

[0044] Operational principle of the present invention is explained asfollows.

[0045] Signal amplitude of the AMR device is given by equation:$\begin{matrix}{{\Delta V}_{pp}^{\cdot} = {{MrW}*J_{MR}*\Delta \quad \rho*\frac{R_{SAL}}{\left( {R_{MR} + R_{SAL}} \right)}*\left( {{\sin^{2}\theta} - {\sin^{2}\theta_{0}}} \right)}} & (1)\end{matrix}$

[0046] where

[0047] ΔV_(pp): peak-to-peak amplitude (V),

[0048] MrW: MR read track width (μm),

[0049] J_(MR): current density passing through the MR device film(A/m²),

[0050] Δρ: magnetoresistive coefficient of resistivity of the MR layer(Ω.m), $\frac{R_{SAL}}{\left( {R_{MR} + R_{SAL}} \right)}:$

[0051] voltage shunting factor,

[0052] R_(MR): sheet resistance of the MR layer (Ω),

[0053] (R_(MR)+R_(SAL)): sheet resistance of the SAL layer (Ω), and

[0054] (sin²θ−sin²θ₀): sensitivity function of the MR device.

[0055] For the same operating current I, there is a signal enhancementby a factor of square of (R_(MR)+R_(SAL))/R_(SAL) comparing an AMRdevice without a current flowing through SAL to that with a currentshunting through the SAL. In a typical AMR device, the shunt factorR_(SAL)/(R_(MR)+R_(SAL)) is as much as 0.7.

[0056] In the case of a SAL electrically isolated from the MR element,the SAL is electrically floating, which could result in electric-popnoise due to static discharge between the MR and SAL. In the inventionillustrated in FIG. 1, we let a small percentage of current flow throughthe SAL. The way to achieve it is to provide electric contact to the SALat the end of the element. With such configuration, the SAL is no longerelectrically floating as there is a small amount of current flowingthrough the SAL. The shunting factor is determined by equation:$\begin{matrix}\frac{R_{SAL}*L_{SAL}}{{R_{MR}*W_{MR}} + {R_{SAL}*L_{SAL}}} & (3)\end{matrix}$

[0057] where

[0058] R_(SAL): sheet resistance of the SAL,

[0059] R_(MR): sheet resistance of the MR layer,

[0060] L_(SAL): length of the SAL, and

[0061] W_(MR): electric trick width of the MR layer.

[0062] We can tune the current ratio by simply adjusting element heightand length. For reference, current MR/SAL sheet resistance ratio isabout 3/7. We can get 2% of current flowing through the SAL by settingwidth of the MR element at 20 μm assuming that our physical read trackwidth is at 1 μm. This shunt ratio renders such a device have muchhigher signal than that of conventional SAL-biased AMR heads with aconducting spacer.

[0063] An alternative approach taught in FIG. 2 is to electricallyconnect one end of the SAL to the MR element. In this case, the SALlayer keeps the same electrical potential as that of one terminal of theAMR device and is no longer electrically floating. The advantage of thisapproach is to eliminate the current shunting through the SAL whilepreventing the SAL from electrically floating. By doing this, we caneffectively eliminate charges building up in the SAL so that theelectric-pop noise in the MR device is prevented.

[0064] Similar concept is used to short a MR/SV (spin valve) GMR deviceto either a top or bottom shield. By doing this, we can prevent theelectric-pop noise due to static discharge between the MR/GMR device andshields. It must be pointed out that such electric-pop noise is afundamental technology challenge for future higher density recording.

[0065] Additional advantages and modifications will readily occur tothose skilled in the art. Therefore, the invention in its broaderaspects is not limited to the specific details, and representativedevices, shown and described herein. Accordingly, various modificationsmay be made without departing from the spirit or scope of the generalinventive concept as defined by the appended claims and theirequivalents.

What is claimed is:
 1. A magnetoresistive device comprises: amagnetoresistive layer; a soft-adjacent magnetic transverse bias layer(SAL); an insulating layer arranged between said magnetoresistive layerand said magnetic transverse bias layer; a conductive layer contactingelectrically both said magnetoresistive layer and said magnetic biaslayer at at least one end region of said SAL element.
 2. Amagnetoresistive device according to claim 1, wherein thickness of saidmagnetoresistive layer is more than 50 Å and less than 400 Å.
 3. Amagnetoresistive device according to claim 1, wherein thickness of saidSAL is less than 500 Å with its moment ratio to said magnetic resistivelayer ranging from 0.6 to 1.0.
 4. A magnetoresistive device according toclaim 1, wherein said SAL is extended beyond active region of saidmagnetoresistive layer.
 5. A magnetoresistive device according to claim1, wherein width of said SAL is 3 to 25 times that of said active regionof said magnetoresistive layer.
 6. A magnetoresistive device accordingto claim 1, wherein said conductive layer comprises a longitudinal biaslayer and a lead layer.
 7. A magnetoresistive device according to claim1, wherein said insulating spacer layer ranges from 50 to 200 Å inthickness, and is formed of materials, such as Al₂O₃.
 8. Amagnetoresistive device according to claim 1, wherein ratio of currentbetween said magnetoresistive layer and said SAL ranges 20 to
 200. 9. Amagnetoresistive device according to claim 1, wherein said current ratiocan be tuned by varying the SAL width.
 10. A magnetoresistive deviceaccording to claim 1, wherein said magnetoresistive device furthercomprises a diffusion barrier layer.
 11. A magnetoresistive deviceaccording to claim 1, wherein said SAL could be a bilayer structureconsisting of magnetically soft film layer pinned by antiferromagneticfilms.
 12. A magnetoresistive device according to claim 1, wherein saidSAL layer is connected to only one end of said MR device and keeps anequal electrical potential to said end of said magnetoresistive device.13. A magnetoresistive device comprising: a first shield; a secondshield; an AMR/GMR device; a first insulating gap layer between saidAMR/GMR and one of said shields; a second insulating gap layer betweensaid AMR/GMR and another of said two shields; a conductive layercontacting electrically said AMR/GMR device to either one of saidshields.
 14. A magnetoresistive device according to claim 13, whereinsaid AMR/GMR device comprises either an AMR device or a GMR device. 15.A magnetoresistive device according to claim 14, wherein said GMR devicecomprises sensing thin films using giant magneto-resistive effect suchas a spin valve, GMR multilayer and spin-dependent tunnelling device.16. A magnetoresistive device according to claim 14, wherein said AMRdevice comprises sensing thin films using anisotropic magnetoresistiveeffect such as a SAL-biased AMR.
 17. A magnetoresistive device accordingto claim 13, wherein said bottom shield is connected to one end of saidAMR/GMR device, and keeps an electrical potential to said end of saiddevice.
 18. A hard disk driver provided with a magnetoresistive deviceaccording to any one of the preceeding claims.